The present invention relates to a device for loading and unloading wafers of semiconductor material such as silicon into equipment for chemical and thermal treatment such as horizontal diffusion ovens.
This invention is adapted for the industry of the production of semiconductor components.
The silicon wafers are transported into clean rooms in plastic boxes containing twenty-five wafers disposed in a plastic cassette with twenty-five positions called a basket, the different positions being defined by slots formed in the cassette. These silicon wafers are treated thermally in horizontal ovens after transfer of the plastic cassette on boats of thermally refractory material such as quartz and silicon carbide. These quartz or silicon carbide boats are disposed manually on a cantilever of silicon carbide in the form of an overhanging blade, or bitubes. Six to eight boats of fifty wafers are the normal load. In clean rooms, it is common to find transfer machines for one, or at most two baskets to a same boat containing thus twenty-five or fifty wafers disposed in twenty-five or fifty slots of the boat. The boat is manually placed on the cantilever following the stage, because the horizontal diffusion ovens comprise in general four superposed stages of which the upper stage is located about two meters off the ground.
This way of proceeding has the following drawbacks:                the presence of the human operator generates particles disposed on the micro-pattern of the integrated circuits, causing an electrical defect after passage through the oven.        The operator by positioning the boats on the cantilevers causes friction of refractory materials generating particles and hence electrical defects.        Moreover, the weight of a full boat, loaded with twenty-five to fifty wafers of one hundred fifty or two hundred millimeters is substantial and renders difficult the loading on the upper stages of the diffusion oven.        
It should also be noted that the manual positioning of the boats on the cantilever is haphazard, which does not ensure repetitivity of the results subject to the insurance of a stable and unique position in the diffusion chambers.
Finally, by human error, the operator can return after treatment the wafers into bad cassettes, which does not permit following a lot in the course of the different steps of fabrication of the semiconductors.
To avoid these drawbacks, there exist elevator systems automatically loading each boat on the preliminarily selected stage. These elevators are supplied or supply an automatic transfer system from one or even at most two baskets.
This practice has the following drawbacks:                The load to be positioned on the cantilever results from eight to ten baskets of twenty-five wafers. The operator must feed the automatic transfer by his presence during the operation of loading or unloading.        moreover, specimen wafers for evaluation of the thermal process must be disposed in precise locations on the boats and recovered after thermal treatment for measurements. The operator positions them on the cantilever manually despite the automatic loading by the elevator.        On the other hand, the load of boats filled with silicon wafers and loaded on the cantilever must be framed with screening boats with a disc of quartz or silicon carbide.        Finally, by human error, the operator can return after a treatment the wafers into bad baskets, which does not permit following the lot in the course of the different steps of fabrication. The same problem arises as to the recovery of the specimens relative to their position on the load.        